Today's increasing demand for more signal speed and bandwidth has stimulated the transition from copper to fiber as the preferred means for the data transfer. A common perception is that this transition can be solved by simply replacing the copper cables with a fiber system. However, such as conversion faces significant technical challenges. For example, not only must the fiber termini physically fit within the same form factor as the electrical contacts, but when dealing with fibers, and, in particular, the nine (9) micron single mode (SM) fiber core, much tighter tolerances are required than those sufficient for copper contact operation. For instances, copper connectors allow the copper contacts to bend during the mating engagement whereas the fiber termini have limited allowance for such a deformation. The reason is that copper contacts need to make only a physical contact (anywhere over the wipe distance) to operate, while the fiber termini requires a precise mechanical axial alignment of the small fiber cores.
For optical operation in a vibrational and dusty environment it is often preferred to use a non-contacting lensed expanded beam (EB) terminus over a physical contact (PC) fiber connection as it provides a more reliable performance under harsh conditions. However, the tight alignment requirements mentioned above still apply. For example, the circular MIL-38999 connector, which originally was designed for copper contacts, and was standardized in the MIL-DTL-38999L document. This widely used industrial connector allows a lateral misalignment of the plug to receptacle cavities of up to 0.50 mm [0.0195 inch] for worst case. While this is acceptable for electrical contacts, such a misalignment will cause serious mating problems for the fiber termini. This can result in termini damage due to stubbing and will most often create unacceptable loss levels.
Typically, the effect of mating fiber termini with lateral misalignment will translate into an angular tilt between the pin and the socket and is one of the largest loss contributors for optical fibers. The effects on single mode (SM) expanded beam (EB) connectors are particularly deleterious. FIG. 1 shows a sensitivity graph of the modeled loss addition caused by angular tilt between an EB SM pin and socket. For example, referring to FIG. 2, a SM EB pin terminus 201 which is about 20 mm long including the crimp eyelet is mated to a SM EB socket 202. If its end is tilted 70 microns (or 0.20 degrees) relative to the SM EB socket axis, the modeling shows that a loss of approximately 1.0 dB is incurred. A slight increase of the angle from 0.20 degrees to 0.25 degrees tilt causes the loss to jump to 1.6 dB.
One approach for accommodating angular offset in SM connectors is disclosed for in U.S. Pat. No. 9,213,147. This patent applies only to physical contact connectors and discloses a specially configured ferrule that narrows as it passes through the orifice of the housing to accommodate angular movement. Applicant recognizes several shortcomings in such a configuration, including, for example, compromised strength in the narrow portion of the ferrule, and the need to produce/machine custom ferrule components which can be prohibitively expensive.
Accordingly, Applicant has identified the need for an SM connector expanded beam (EB) design that will compensate for angular tilt and lateral offset without the preparation of exotic and complicated parts. The present invention fulfills this need among others.